Auditory perception of a false killer whale (Pseudorca crassidens) and a Risso's dolphin (Grampus griseus)

A deficiency for scientific evidence exists for marine mammals, with only 12% of odontocete species having auditory threshold information documented and no threshold information for any mysticete species. The opportunities for experimental research in controlled environments are so rare, and it is important to evaluate the scientific methods utilized in marine mammal science.; Both behavioral and auditory evoked potential (AEP) audiograms of a false killer whale (Pseudorca crassidens) were measured using the same subject and experimental conditions. The objective was to compare the auditory thresholds collected by psychophysical and electrophysiological techniques. The behavioral and AEP data were reliable and repeatable. Behavioral thresholds were lower than AEP thresholds. However, AEP audiograms were completed in shorter amounts of time with minimum participation from the animal. These threshold results indicated that behavioral and AEP techniques can be used successfully to measure cetacean hearing sensitivity.; These AEP techniques were used when an infant Risso's dolphin ( Grampus griseus) was rescued in Portugal, and an AEP audiogram was measured. The stimuli used were sinusoidally amplitude-modulated (SAM) tone-bursts, and AEP responses were analyzed to quantify the animal's electrophysiological response and hearing thresholds. The animal's audiogram showed a wide range of hearing sensitivity and possibly redefined the auditory thresholds for this species.; The detection of complex tones by a marine mammal has never been documented in the scientific literature. A psychophysical experiment examined whether a false killer whale can discriminate pure tones from complex tones. A secondary objective was to determine the minimum intensity level of each harmonic component required to make the discrimination. Conducted with a go/no-go modified staircase procedure, the results from this discrimination task demonstrated that the false killer whale was able to discriminate a pure tone from a complex tone with up to five harmonics, and that discrimination thresholds for each harmonic combination was measured. Both frequency level and harmonic content may have contributed to the discrimination capabilities of the animal. This was the first attempt to investigate the ability of a marine mammal to perceive and distinguish harmonic combinations of sound.